You probably don't know what ISO means – and that's a problem

Whatever camera or phone you have, it’ll report the ISO value it used to take its photos. Despite its ubiquity, ‘ISO’ probably doesn’t mean what you think it does. Worse still, it may be holding your camera back, both in terms of the images it takes and in the tools it provides you. This means it's potentially holding your photography back, too. Part of the problem stems from the fact that ISO sounds like something you were already familiar with.

At first glance, ISO settings look just like the sensitivity ratings used for film (to the extent that there are some people who still refer to ASA: the US standard incorporated into the ISO standard for film). But ISO in digital isn’t the same as film. it’s essentially a metaphor for the way film sensitivity worked, if you got it processed in a minilab machine. This is a problem.

It causes confusion

The apparent familiarity and simplicity of ISO setting leads to a number of common misunderstandings. Despite what you may have heard or read, changing the ISO of your camera does not change its sensitivity.

ISO changes the lightness of the final image but it doesn’t change the fundamental sensitivity of your sensor. Nor is it an indicator of amplification being applied: although many cameras do increase their amplification as you increase the ISO setting, this isn’t always the case.

"Why can't I use ISO 100 in Log mode?" The answer is that a log gamma curve is so flat that it requires very little light to achieve middle grey, which means it's considered a high ISO. Strictly speaking, though, you can't really calculate an ISO value for log at all, since the standard is based on a different colorspace and gamma. It's a similar story for Raw.

This may sound like semantic nit-picking, but it causes a lot of misunderstandings. It’s widely thought that the additional noise in high ISO image comes from the ‘background hiss and hum’ of the sensor’s amplifiers. This feels right: we’ve all heard more noise if we turn up the volume on an audio amplifier. Unfortunately it’s simply not true: most noise actually comes from the light you’re capturing, so it primarily depends on your shutter speed and aperture.

The ISO standard doesn't specify that amplification needs to be used, nor does it specify what happens in the Raw file

The ISO standard doesn't specify that amplification needs to be used, nor does it specify what happens in the Raw file. All it does is relate initial exposure to output JPEG lightness, however that is achieved. The only thing you can be sure of, at the Raw level, from an increase in ISO is that if it prompts a reduction in exposure, you'll collect less light and therefore see more noise for each tone from the scene.

There's an ISO standard that's slightly more pertinent to Raw files, which looks at when the sensor becomes completely saturated, but this doesn’t correspond to the standard used by your camera. So next time you see a graph comparing ‘Manufacturer’ and ‘Measured’ ISO, what you’re actually looking at is the ‘JPEG ISO’ vs ‘Saturation ISO.’ Any differences between the two mainly tell you how many stops above middle grey the manufacturer's JPEG tone curve is designed to deliver.

It encourages poor exposure

As well as giving a false sense of simplicity, ISO’s increasingly tenuous attempt to mimic film ratings can mean making poor use of sensor response.

Film (particularly negative film) has a very distinctive response curve that gives lots of latitude for recovering highlights. Digital is very different: it offers a much more linear response but with a hard, unrecoverable clipping point in the highlights. And no, your favorite software doesn't really recover completely clipped highlights from your Raw file*.

This graph shows the signal-to-noise ratio (essentially the noisiness) at different brightness levels of film and digital. The film response peaks and then gradually declines, with plenty of scope for recovering highlights from the right-hand side of the curve. The digital response rises to much higher levels than the film, then cuts-off abruptly. So why would you expose these two media in the same way?

And yet, despite these differences, the digital ISO standard is based around ‘correctly’ exposing JPEG midtones**. A 2006 update to the standard gave manufacturers some flexibility in terms of how many stops of highlights they wanted in their JPEGs above middle grey***, but it still encourages exposure based on midtones, with a pre-set number of stops above this for highlights.

That’s not the best way to expose digital. The best results are achieved by giving as much exposure as possible without clipping the brightest tones you care about: a process called ‘exposing to the right.’ This maximizes the amount of light, and hence signal which, in turn, optimizes the signal-to-noise ratio (essentially ‘noisiness’).

And yet, by worrying about the JPEG middle grey, cameras end up giving every image the same number of stops for highlights, even though this is wasted in low DR scenes (that highlight space isn’t used and exposure is lower than optimal) or insufficient in high DR situations: the lovely colors of the sunset you’re shooting are lost, unrecoverably, to clipping.

Fujifilm’s DR modes essentially give you a choice of amplification and tone curve combinations that include different amounts of highlight information. These end up being rated as different ISO settings.

The ISO 200 / DR 100 example on the left has the least noise. The ISO 400 / DR 200 image has a shorter exposure, bringing more noise, despite having the same amount of amplification as the ISO 200 image. This low level of amplification means it has retained more highlight information than the ISO 400 / DR 100 image on the right, which used the same exposure but more amplification.

This problem isn’t easily solved: there are times that exposing-to-the-right will result in noisier midtones than you want. In these situations, you have to let the highlights go. However, fixating on JPEG midtones isn't helpful.

It warps camera development

This brings us to the biggest problem with using a clumsy metaphor for film sensitivity as the way of setting image brightness in digital: it means we aren’t given the tools to optimally expose our sensors.

ISO ends up conflating the effects of amplification and of tone curve, meaning you have to do your own research to find out what your camera’s doing behind the scenes, and what the best way to expose it is.

We aren’t given the most basic tools: Raw histograms or Raw clipping warnings that would help optimize exposure

The preview image your camera gives, the histograms it draws and the exposure meters and guides it offers are all based on JPEG output and their midtones, because ISO says that’s what matters. This means we aren’t given the most basic tools we need: Raw histograms or Raw clipping warnings that would help optimize exposure. It means no development has been done to create more sophisticated tools that would help you judge the quality implications of exposing to the right, and when to let the highlights go.

In short, ISO is an increasingly shaky metaphor that promotes misunderstanding, obscures what your camera is doing and robs us of the tools we need to get the most out of our cameras. Isn’t it time for something better?

Thanks to Bobn2 for feedback and fact-checking

* Highlight recovery sliders usually rely on only one of the color channels having truly clipped, and try to guess the value of the clipped channels, based on the remaining, unclipped one, so tend to be limited in their effectiveness. [Return to text]

** We put the word "correctly" in inverted commas because the more you think about it, the harder it becomes to pin down what 'correct' exposure might be. If you're certain that you know what 'correct' exposure means, then you should probably check through the assumptions that underpin it. [Return to text]

Comments

RB: "ISO changes the lightness of the final image but it doesn’t change the fundamental sensitivity of your sensor."

How does it raise the lightness without greater sensitivity to light, other things being equal?

RB: "Nor is it an indicator of amplification being applied: although many cameras do increase their amplification as you increase the ISO setting, this isn’t always the case."

This entails that the prior sentence may be wrong most, if not all of the time. Amplification and increased sensitivity seem complementary, or the distinction is cloudy. And can one know a camera's ISO amplifies or not? DPR's reviews don't seem to disclose one way or the other. The manufacturers are also rather tight lipped about their sensor technology. All we see are the ISO ranges and some noise comparisons.

The article does not explain why some cameras' high ISO performance is better than others. What is the difference between the Sony A7s series and prior or competing devices?

Yes I agree with this. The original article is confusing and incomplete.

If you up the ISO control on your camera, whatever that actually may mean, then you get exposures with less light when you stop down and/or use a faster shutter speed. I accept that the sensitivity of the sensor cannot/does not change but the result looks pretty much the same so something has changed. If it is not the electronic gain then there must be some magic going on and I thought alchemy was a fiction long since put to bed.

Any noise in the image is from the camera. It is ridiculous to suggest the image light includes any noise. If there were any noise there, we would see it with our own eyes looking at the subject matter in real life, but we don't. The powers up there in the sky may refuse to allow Mr Butler in for making a suggestion like that.

When you crank up ISO, your camera can: - Increase analog amplification, i.e. amplify analogs signals coming from the sensor before they are converted to digital values. This is what most camera used to do in their 'native ISO range'. - Brighten the image after analog signals are converted to digital values. If you shoot RAW, it will *not* not affect the RAW data; just change a metadata value that your RAW software will take into account (which is good because it gives you headroom in the highlights). If you shoot shoot JPEG the camera will process the data applying a multiplier (or something a bit more refined maybe.. ).

Modern cameras can use a combination of both, including in what it is supposed to be their 'native ISO range'..

Note: I willingly passed over multigain sensor design, because at the moment I see how it impact the sensor performances, but I don't fully understand how it works.

Think of what a camera does as painting by numbers. The numbers in the raw file are exposure values, pixel by pixel. The camera chooses a shade of paint according to each number in the raw file. ISO chooses which paints correspond to which numbers. Increase the ISO and you lighten the paints. No change in 'sensitivity' required.

The entire article is highly confusing because it is written from within a certain thinking context, but fails to properly explain that context. Especially for the technically less interested, this is then bound to become a garbled mess of non-information. One major problem, and also one of the main reason for most of the discussions, is terminology: What do you understand by term XYZ? And that is also one of the main issues with this article: It fails to clarify that to the point that everyone can follow it.

For example, whenever it is about ISO and digital, you MUST explain the term "sensitivity". That is not really done. There is often the talk about "ISO sensitivity", and coming from that angle it is not clear why cameras have a fixed "sensitivity", it just doesn't make sense.

The other view is from processing signals. We have a sensor, and it converts light into electrons and further down into potential/voltages which are then converted into digital numbers. [cont...]

[cont...] From this point of view "sensitivity" just means how well you can do that transformation of light into electrons, how "sensitive" the sensor is to light. What you do after that is of no relevance to the "sensitivity" anymore.

@keepreal: There are 2 noise sources in digital photography: Shot noise and "read" noise (which is a conglomeration of various different noise sources in the signal processing chain).

Our own vision system is really good at "handling" the shot noise component. Just because you don't perceive it doesn't mean it is not there. We are not able to see or hear UV, IR, or all these radio waves, yet these are there, too.

"For example, whenever it is about ISO and digital, you MUST explain the term "sensitivity."

The concept of sensitivity comes from film. In the days of film, you couldn't just pick any roll of film you wanted to shoot in any lighting setting you wanted. The reason why is that certain films had a certain level of sensitivity to light (or ability to pick up light better than others). This sensitivity was measured in terms of ISO. The higher the ISO number, the more sensitive the film. The lower, the less sensitive.

For example, say you wanted to shoot a family picnic outdoors on a sunny, cloudless day. You pick a roll of film with 100 ISO. As long as you shot in broad daylight, your photos would turn out perfectly exposed. But let's say you decided to take pictures at night with this same roll of 100 ISO film. Unless you used flash, the pictures would come out horribly underexposed because IS0 100 film wasn't sensitive enough to pick up the dim lighting of your environment.

Because ISO affected how you could shoot in lighting situations, you had to use different ISO films if you anticipated shooting at different times of day or indoors versus outdoors. For example, going back to the picnic situation, if you knew you were going to shoot outdoors in bright light and then later at night, you'd bring along a roll of ISO 100 film for broad daylight and maybe 400 ISO or higher for late evening.

It's the same exact concept in digital. The higher ISO settings on your camera enables you to you capture lighting in increasingly dim lighting situations (twilight, candlelight, indoors, etc.) without relying on flash or needing a faster lens.

So, think of sensitivity as that, as the increased ability to capture light as it gets fainter and dimmer.

As for "fixed sensitivity", that's never made much sense to me. Even if it were technically true that sensors on cameras have a fixed sensitivity, the combination of the sensor and technology that creates digital ISO makes ISO function exactly as it did in film.

To put it another way, we can argue that theres no such thing as varying sensitivity in sensors because they're "fixed", but in the end of the day, if I'm shooting a sunset and I don't want motion blur from ships passing on the water and I don't have a tripod or surface, I need to boost the ISO. I can't just shrug my shoulders and go, "Well, there's no such thing as ISO speed (and it's all a shaky metaphor, anyway), so I'll just shoot this scene at the widest aperture and the slowest exposure without a tripod, and everything will turn out okay."

My entire point is that it doesn't behave exactly like film. I'll agree it's a similar concept and that it appears to work in a similar manner but that's my concern.

There are many cameras on the market that offer two different ISO settings but use the same underlying amplification. The only difference is the exposure encouraged by the meter and the tone curve used for the final JPEG.

There are cameras that provide different ISO settings by using the same level of amplification then mathematically doubling the Raw values for the higher ISO setting (some write these doubled numbers into their Raw files, others have a metadata flag that tells the Raw processor to double all the values).

ISO is not necessarily gain. The ISO value tells you that it'll put middle grey roughly where you'd expect it, in your JPEG. That's all. It tells you nothing about the Raw file, nothing about the highlights of your JPEG and has a surprising amount of leeway around middle grey lightness.

The article is useful to me for one very simple statement: "changing the ISO of your camera does not change its sensitivity". Somewhat more obtuse is an implication that it is best discussed vis-a-vis an analog signal that is created after the photo is snapped. Very interesting as the literature is awash with different arguments one way or the other. I especially became intrigued when one of the replies (multi-part) implied it gained up the signal to the A/D in order to ensure all the discrete bins were occupied. Anyway, not sure about that last part. But, I think the article has begun clearing up my confusion over this topic (I hope). Thank you.

Great article! For once, the myth that ISO in digital is the same as ISO for film is exposed.I use mainly a Oli EM5MII with ISO set at 400, even though a lot of sites claim this camera has a "fantastic" setting of 100ISO for "low-noise".Yeah, sure...Since I started using 400ISO as the base setting, no more blown highlights, no more problems with "noise" and superb DR. Yeah sure: I shoot in RAW and need to process all images and recover the odd bit that is too dark - and I still need to be careful with the metering. Sue me!...

The OM-D E-M5 Mark II has a native sensitivity of ISO 200. When you choose ISO 100 the sensor is overexposed by one f-stop and you lose one f-stop worth of dynamic range. These days, many cameras offer ISO settings below the sensor’s native sensitivity even when there is little advantage to that. Overexposing the sensor – and tweaking the raw data so the exposure looks normal – does reduce noise, but there is very little noise even at ISO 200 and the loss of dynamic range typically outweighs any slight advantage with regard to SNR.

Exactly when, in photographic history, did "ASA" become "ISO"? I remember a very simple rule when using any film (Kodachrome 25 was my favourite until it was discontinued): the ASA/ISO number was your approximate shutter speed for an aperture of F16 in the middle of a bright sunny day. And even when shooting with my (100% manual, meterless) Nikonos IV, applying this rule - and then adjusting according to the time of day and weather - gave me an exposure success rate that shames many a modern "evaluative" metering system. Sure, I had my Weston EuroMaster II to hand when things got tricky (and still have!), but ASA = Shutter at F16 at Sunny Midday is all anyone needed know to get decent exposures!

ISO in digital means that your JPEG will probably still look about right if you continue to use the Sunny 16 rule. What's going on behind the scenes and whether it's the optimal exposure for your camera is anyone's guess.

Minimum depth of field you want + maximum amount of blur you want at base iso will goven any camera settings over ettr. If that happens to be for example f8 1/250 at base iso then there is no scope for ettr. Any opening up of aperture or slowing of shutter speed beyond the desired parameters will have a far more detrimental effect on the image than an exposure to maximise the sensor!

The only difference is that in film sunny 16 calculates f stop whereas in digital it will calculate exposure compensation from base iso.

Richard, I know, ASA was a linear scale (double the ASA meant half the shutter speed, or 1 stop less, for a given exposure) where as DIN was a logarithmic scale, base 10, with 3 steps per doubling of sensitivity. Just as in decibels, etc. So my rule-of-thumb worked with ASA (the equivalent of today's "ISO" setting on a digital camera), but for DIN, required a look-up table!

While i agree with the article i think there is one fundamental similarity - for a photographer iso calibrates the meter to the film or sensor. In both cases after that then changing the iso dial acts as an exposure compensation.

However, the film photographer will recalibrate his meter more often because he can use different films whereas a digital photographer typically only uses the one sensor in their camera. Therefore that dial is pretty redundant on a digital camera except as a +10(or whatever) exposure compensation control.

I probably should have been or, at least, in 2006 when CIPA significantly broadened the definitions.

It's only recently that advances in sensors (to allow near ISO invariant shooting, for example) that it's become increasingly obvious (to me, at least) how limiting it is to merge the effect of tone curve and amplification in a distinctly opaque manner.

Why do different cameras have a different base ISO, even if they use (almost) the same sensor? E.g. Fuji's and Olympus' cameras have (all?) ISO 200 as base ISO, while other cameras with Sony sensors (e.g. Sony's and Nikon) often start at ISO 100?

Even then, if I compare my Canon G7x II to my Fuji X-T1 (1-inch to APS-C), I see that given the same FoV, exposure time and aperture (I'm neglecting equivalent aperture here), the ISO value choosen by the auto ISO function differs by a factor of 2 (e.g. G7xII: ISO 200; X-T1: ISO 400). Why is this?

@Sacher Khoudari Since ISO is just defined as a middle gray in the JPEG as described in the article with some extra flexibility of what should be considered middle gray, ISO according to Canon doesn't need to be the same as Fuji ISO.

I reread this and now I understand what ISO is not but not entirely what it is, just that it has little to do with ISO for film.

No matter, I always used to spot meter a mid tone with film and adjusted my film processing technique including the developer, development and ISO to peg the highlights within the range of the film and optimise gradation from highlights to shadows. Until recently, I applied a similar technique with digital, spot meter on a mid tone and exposure bracketing when the highlights would be burnt out or shadows too dark and noisy.

I have now changed that, metering on the brightest tone and relying upon the RAW file to record darker tones from there, so no clipped highlights, Then when necessary, I still exposure bracket to add frames to deal with shadows when they are too under-exposed in the first frame.

So my only recent change is to spot meter the highlights and set EV +3. Unfortunately, action photographers relying upon auto exposure cannot easily do this.

Short version. The film rule was "expose for the shadows and develop for the highlights". The digital rule is "expose for the highlights".Intuitively true, because film produces a negative image and sensors a positive one.

Stating the obvious for most of us, this film rule is only true for negative film, not for positive film like slide/transparency film. For positive film, the best exposure depends on intended usage, whether for projection or for Cibachrome/Ilfochrome printing.

If we do not have the tools to 'properly' expose* our images - what tools would remedy that? Is it just the Raw histogram and/or Raw clipping warnings, or are there other tools? Would that be a 'Live' histogram or highlight clipping or a post exposure one? Does any camera provide some or all of these tools. What about professional/broadcast or cinema cameras?

LOL. Nikon calls it D-Lighting. To start. With many other in-cam and pre-shot (or some post) settings. In fact: I programmed mine to match Porta 400 film looks; for sunny portraits. It's just a touch greener than the standard Portrait setting and with D-Lighting ON. Blondes in warm sun work well.

You can get away with no computer editing if you know what you're doing (with a decent sensor).

Oh yeah: You compare your target look to your camera output on a calibrated monitor. The back of camera screens are slight off when you get nit picking. So for example you want your picture to look like Portra 400 on your calibrated monitor; not the back of your cam.

It's just how they make them; for cost reasons, no doubt. It's more about the technology-type and materials. Not far off; but off.

Just pick a preferred film look as scanned (online pictures) that you like. Set (in cam) what comes out (or will come out) of your camera to match your target film picture on your monitor.

Even if you did none of that then you could instead just play with the film looks in Gimp; plus adding GMIC under enhancements and new film. All free and in addition to what you got. If you have consistent and well exposed base photo to edit thhen you could use it like preset. If you don't it has optional adjustments for varying exposure's and situations.

Everybody's a freak-en' genius. But they still have not matched negative films rolling highlights. Still not giving control OPTIONS and still not beating DSLR /OVF and battery life. Today's best engineers can figure out how to do all that.

And I know how to SIMULATE film and highlights(with Raw and then Gimp+). I can do several things to a digital picture to approximate what was good about film.; but that's time spent each shot. Too much time. Not that film doesn't have negatives (get it?).

But you're more interested in bragging rights and brick sized systems; without total value. And WiFi.

What about photography?

Tech or no; it's a good article. And I know we all need to back off on being overly technical. But technically; a good heart felt picture requires many technical attributes to make what you envision. Not just get lucky with. The camera still matters and this is why we could use a better one in better combinations (of photo making goodness).

This is a patent demonstration of how knowledge and teaching ability are two totally distinct things. The author know the Physics behind the sensors, but doesn't grasp what is important for photography and what is not.

Additionally, he misses the importance of the development process (in-camera or using softwares such as Capture One, Lightroom, etc), and how they work.

A big problem for writing an article like this is that to really understating the issues requires a significant background in photonics (the physics of quantum light and the true nature of noise (uncertainty) and sources of noises, esp Poisson vs readout) as well as some engineering principles.

Without this background knowledge, a short article is either gobbly-goop or a useless/misleading oversimplification. Any attempt to impart the necessary background is doomed because it requires serious study and thought on the part of the reader (and quite a few more words in the article).

I doubt that this article will clear up the confusion and is likely to contribute more mythical "understandings".

Yes, there is a lot of misconceptions about ISO speed in digital cameras, like "increasing ISO results in additional noise". One can often see an expression "high ISO noise", for example, or references to a mythical "exposure triangle". If you read the comments under this very article, you may note that some readers think the noise accompanying high ISO shots comes from an amplifier.

Agreed, justnuaces. It's not a problem if one understands the practical implications. Higher ISO allows faster shutter speed or smaller aperture but brings more noise and less DR. That's it. If one wants to understand the science beyond that, then great, but it's not required.

Higher ISO speed brings less or equal amount of noise for the same exposure. Noise comes from low exposure, not from high ISO speed. That's why it makes sense to set the maximum possible exposure first, and not to rely on ISO speed to "compensate" for lower exposure.

Iliah Borg, you're right, and I'm not saying the Author isn't well informed about the topic. Nothing in the article is wrong, but as minababe points out it's written with for a target who couldn't understand some implications. And it isn't oversimplified. I have some background in Physics (long ago, and I never worked in the field), and I really appreciated this article. But for one who doesn't know some Optics and Electronics, I think this page contains more questions than answers, and creates doubts.

@justnuaces I am afraid I can't follow you with your arguments. You think the article requires some knowledge in Optics and Electronics? At the same time it's written for people who "couldn't understand some implications"? The author " doesn't grasp what is important for photography"?

I consider an optimized exposure as very relevant to photography. And that requires a basic understanding of how light is turned into grey values of different colors in a raw file. A couple of months ago I have been one of those (many) people assuming that ISO is directly related to sensor amplification. And I didn't know that ISO is defined by the middle grey of the final jpeg. It explains a lot for me.

With a mixed target group of low educated and rather simple minded to highly intelligent and highly educated people it's impossible to address everyone.

It doesn't change anything because digital ISO works exactly as it did in analog ISO.

This article reminds me of how in art class, professors would try to teach me painting by insisting that I didn't understand that objects had no color; they were just colorless objects bouncing off specific wave lengths from the electromagnetic spectrum. Well, maybe that was true but in the end of the day, you use red paint to paint an apple and green paint to paint grass. All of this technical and scientific jargon didn't mean a hill of beans.

What it changes is you now know there's a disadvantage to just thinking about "cranking up" camera ISO parameter. The goal is to use the lowest practical camera ISO setting for what you're trying to accomplish.

"What it changes is you now know there's a disadvantage to just thinking about "cranking up" camera ISO parameter. The goal is to use the lowest practical camera ISO setting for what you're trying to accomplish. "

So, are you telling me that people like you and the author don't know that since time immemorial, this is *exactly* what photographers have been doing? Always using the lowest ISO as possible but then compensating by using longer exposures, tripods and faster lenses?

""This article reminds me of how in art class, professors would try to teach me painting by insisting that I didn't understand that objects had no color; they were just colorless objects bouncing off specific wave lengths from the electromagnetic spectrum."Just because you weren't interested in color science, and all the tools available to form understanding, doesn't mean others in your class weren't. I always prefer more knowledge, to less.

With some hypothetical future camera:In some 'ISO' submenu, you could select 'analog amplification', 'digital correction' or 'auto'. - 'Analog amplification' would be what you get with current camera. - 'Digital correction' would stick to 'native ISO', but would add a metadata in the RAW file AND would output JPEG with correct brightness SOOC.- 'Auto' would be whatever 'special sauce' the manufacturer wants (e.g. to take advantage of multiègain sensor design).'Digital correction' and 'Auto' would offer best of both worlds: simplicity AND correct JPEG output AND more headroom in the highlights when 'developing' the RAW file.Cherry on the cake, you can bundle that with 'dynamic tone mapping' so JPEG SOOC apply a gentle 'roll-off' to the tonal curve in the highlights if necessary and they are not blown out.

I went to a school to LEARN painting. I wanted to LEARN how to pick up a brush, learn how to pick and mix the right pigments, and how to apply them to a canvas so that if there were, say, a bouquet of flowers, I could paint them as they were.

I DIDN'T learn how to paint because the science of color and light physics has nothing to do with the actual process of painting.

This article is like that class. Its entire premise is based on this idea that we were all wrong about ISO and it was going to "school" us. Instead, it lapsed into the technology and mechanics behind cameras.

As for your statement that you prefer more information, not less, I ALSO prefer more information, not less. But the information has to have practical application and be accessible. If it's neither, then it's the same as not getting any information at all.

I understood your point, Minababe...I simply disagreed with it. "I DIDN'T learn how to paint because the science of color and light physics has nothing to do with the actual process of painting." Nonsense. It has to do with seeing. I repeat: many students want as much info as possible. There was nothing wrong with the class --it wasn't the class for you.

@caravaggio, I think most of us already knew that ISO should be set to the lowest possible setting to minimize noise. My question is, how does understanding the variance between ISO and the old ASA modify the need to crank? I appreciate the effort that went into the detailed explanation, but I came out of this not sure if I gained anything of practical application.

Phone cameras already do this. The problem is that you need a video feed covering the whole sensor to identify the highlights. That's why it would only work with mirrorless cameras or in live view, unless your matrix meter covered the whole image area.

* Highlight recovery sliders usually rely on only one of the color channels having truly clipped, and try to guess the value of the clipped channels, based on the remaining, unclipped one, so tend to be limited in their effectiveness

If this is the case then ETTR where we think we are pulling back highlights maybe this doesn't work so well. As per sometimes when I use ETTR and really 'go for it' so that it looks clipped in camera all over the shot I pull back in the software (RAW), the blue skies are lets say not the right colour. I've started going easier on the ETTR since because of this apparent false colour (this is with the latest sensors too, D810, D850). Thoughts?

Pulling back highlights will not be sufficient. You have to dial back the exposure slider in Lightroom as well. Than colors start to look saturated again.But it's a very tricky exercise for me. There is always something that will not look right when I'm doing ETTR. Yes you get less noise that's obvious but the color saturation and tone seems to be off.Maybe I have to get deeper into it and get to know my camera better. All in one ETTR is not an easy trick for better photographs.

I did not mean pulling back the highlights by purely playing with the highlight slider, (because that would not be proper working of an ETTR file) of course I meant exposure, locally in areas required with a grad, radial filter, brush etc, sometimes globally. Even so, it sometimes still does not look right colour or tone wise in the pulled back areas which where not clipped but pushed extremely close to being so at the time of capture. And I'm ensuring nothing is clipped as the histogram in lightroom and the white warning areas are not displayed on any white patches on import. So for me it's a strange phenomenon as a ETTR shooter.

Could it be pushing so close to the right during capture is messing up the colour or tonal data in these so very nearly clipped areas and giving me a weird effect when pulling them back?

I've done side by side tests, file "averagely" exposed the way the camera thinks it should be in matrix metering, and brought that file up with exposure bias in post in the shadows enough for a realistic picture, colours in sky are okay, as captured of course. Then I've done the same scene ETTR with pulling it back down in post a lot, the colours in the sky are not the same...I cannot work out why this is.

I still think that's inherently wrong Eric. For the most part, no matter the sensor ETTR is going to stop those noisy shadows looking bad when pulled up. And pulled up a lot they will need to be if you are really doing what you say. Let alone this, it's not just noise, it's zombie like colour in those shadow areas if we go crazy with the pulling. Sensor saturation is everything...

SHUTTER SPEED.One topic that I think deserves coverage is Shutter speed. Film relied on exposure to an amount of light (photons) which was determined by the aperture & shutter speed in which there is a reciprocal relationship

CCD & CMOS are different CCD charge a capacitor integrating time & qty. CMOS use a photodiode.

Exposing film results in changing the sliver halide crystals, the larger number of photons hitting the film (time & qty) the greater the change in the crystals. Digital sensors I don't think work the same way. The electrical signal (voltage) generated by a CMOS pixel in response to be exposed to light is the same regardless if you expose it for 1 sec or 1/1000 of a second. Changing the aperture will vary the number of photons & the voltage generated but changing the shutter speed just lets the camera read the signal for a longer period of time - If you generate the same voltage during a 1/1000 as you do in a 1 sec exposure - why the longer exposure.

"CCD & CMOS are different CCD charge a capacitor integrating time & qty. CMOS use a photodiode".Not really. Both CCD and CMOS use a 'photodiode' to collect charge resulting from the photoelectric effect and both use a MOSFET source follower to read that charge. The difference is how the charge gets to the source follower. In a CCD, it is shuffled along a row of pixels by moving the potential well in which it's trapped. In a CMOS there is a source follower in every pixel (or sometimes shared by a group.

"Exposing film results in changing the sliver halide crystals, the larger number of photons hitting the film (time & qty) the greater the change in the crystals."Film uses the photoelectric effect just like digital. The released photoelectrons reduce silver halide to silver, and the silver atoms form a catalyst which allows the developer to reduce the whole grain. It's an all-or-nothing digital style effect, if there are enough silver atoms, the whole grain gets reduced, if there aren't, it doesn't. The density reflects the proportion of the total number of grains that have been reduced to silver, not the proportion of each grain that has. In that sense film is more 'digital' than digital.

"Digital sensors I don't think work the same way. The electrical signal (voltage) generated by a CMOS pixel in response to be exposed to light is the same regardless if you expose it for 1 sec or 1/1000 of a second."Not the case, the charge accumulated on depends on the number of photos, it doesn't matter what he that number was produced by a long exposure time or a wide aperture. The equivalence of exposure time and aperture with respect to exposure is a basic tenet of sensitometry, and applies to all photographic media.

My suggestion to manufacturers:Give us an additional indicator in EV that shows latitude before RAW clipping, e.g. EBC -0.7 (=exposure value before clipping). You could then easily decide, whether you want to change A or S for optimized exposure or not.

This would be used with RAW primarily, but could even be implemented for OOC JPG with an option in the settings like "Auto EV" that shifts an image with EBC+/-zero to a middle gray value before saving the JPG file.

Maybe I should write Olympus about his. I think they would be innovative enough for doing this and their list of settings can easily handle a few more. ;-)

Nice if somewhat detailed article. My practical take away would be to avoid highlight clipping and therefore under expose - I always and by default bracket every exposure something that would be expensive to do with film. One practical camera feature would be a highlight exposure setting i.e. the camera setting the exposure just below the highlight clipping point.

Not really sure I buy the argument that the noise comes from the image, however we all know that a higher ISO results in more "noise" visible in the image and therefore have a practical work around.

It would be interesting to add colour positive film to the chart. Shooting with Kodachrome or Ektachrome never offered much exposure latitude.

Clip highlight regions that are unimportant to the photograph's purpose. One example could be specular sunlight reflections. There is no useful information in these reflection. When they are intentionally overexposed the S/N for the shadow regions improves. Of course, gross overexposure could produce artifacts. This is how come I also bracket exposures by default.

I like the ISO speed concept, it’s a useful reference, but one thing I agree with is ditching ISO nomenclature when it doesn’t actually reflect a genuine increase in base sensitivity. Eg If ISO 800-12800 are all deriving from the same initial base sensitivity/amplification then just call it 800 and tag it with subsequent “push”. Same as with film, where you denote +1, +2 etc to denote a post-exposure push.

I would much rather know sensor is exposing at 800 speed and subsequently pushing things by 3 stops than be told it is exposing at 6400

Rearding various "we don't care we own D850/A7RIII cameras" comments, given the huge DR of modern sensors, I fully understand that wedding/sport/... pros equiped with cameras with large sensors won't bother and focus on JPEG exposure to provide a quick feedback to clients. But for regular people using 1", M43 or even APSC, exposing to the right permits to significantly improve IQ : more that you can achieve by simply buying a new camera !

Yeah the camera you use matters. That's why you have to practice and find out how much of a difference exposing the the right makes in a given situation,how your meter handles different scenes, and where the clipping line is in the raw vs jpeg. For the first years of my photography I was stuck with a Canon p&s using CHDK to make it shoot dngs. Exposing to the right was REQUIRED in order to not have a noisy mess in the sky and other smooth one color surfaces even at base ISO in broad daylight. My D800 allows for far sloppier exposures. Interestingly the meter in my S7 Active seems to expose more to the right more an do better job of balancing shadows and highlights in a HDR scene than my D800 does.

"The best results are achieved by giving as much exposure as possible without clipping the brightest tones you care about: a process called ‘exposing to the right.’ This maximizes the amount of light, and hence signal which, in turn, optimizes the signal-to-noise ratio (essentially ‘noisiness’)."

ETTR is only optimal if you are shooting and post-processing Raw. JPEGs should be exposed as close to the intended final output brightness as possible: this is because the JPEG coding is non-linear (Gamma), so both amplification and attenuation in PP degrade the image.

Also, in low light situations say night no-flash handheld street photography, ETTR is not a concern at all. Instead best combinations of shutter speed & aperture for desired effects, while keep ISO down for low noise, a delicate balance.

My personal rule of thumb is exposure as long as possible to not blur (or unless I want intentional blur), and aperture as wide as possible to not misfocus. Then ISO do it's auto setting, whatever I get.

"This brings us to the biggest problem with using a clumsy metaphor for film sensitivity as the way of setting image brightness in digital: it means we aren’t given the tools to optimally expose our sensors.

ISO ends up conflating the effects of amplification and of tone curve, meaning you have to do your own research to find out what your camera’s doing behind the scenes, and what the best way to expose it is.

What I take away after reading this article is "the more i learn, the more I find out I don't know". This could all be so stressful if I allowed it, but for that the majority of cameras still have an Automatic setting.

Funny that the article bases its arguments on negative film having a very different response to digital, yet it shows a photo of provia 100F, which is slide film with a very SIMILAR response to digital.

Seems to me we had shutter speed & aperture for ages. Then ASA & DIN, later ISO, came along just to make everyone's photo the same brightness. ISO has to accommodate all possible brightness factors except shutter speed & aperture. ISO has to be a vague, cloud-like standard.

No. That is what you take ISO to mean. To me it's a guide and nothing more. Unless you can show the manufactures a better way to implement the raw exposure, there isn't any way to improve. So lead the way.

Wow, does all this info change the fact that you should only bump up your ISO to gather more light if changing your shutter speed, aperture is not an option.. and the higher your ISO the more grain will be in your image...

It was never a fact that increasing ISO gathers more light. The light received at the sensor at the time of capture is all the light you are ever going to gather. Post-sensor signal amplification or scaling affects the values written to the file, but they never increase the amount of light gathered.

Increasing output image brightness by increasing ISO will result in a noisy image if doing that causes you to 'underexpose' (gather less light).

I doubt that anyone who used both film and digital believed ISO for film and ISO for digital were the same. It's just that very few sat down and thought about the implications of the differences between them, as this article suggests.

There is no 'requirement' to understand it. If you are happy with the quality of the image files you produce in the absence of understanding, then just keep doing what you're doing. The article provides a tool that can be used to minimise image noise - if that didn't concern you prior to the publication of the article, it needn't concern you now.

Fair enough. But some respondents further down have written similar things and don't appear to be joking. I understand why someone might be exasperated if they think they are being 'forced' to learn something they don't want to, but it's an opportunity not a directive.

I remember fondly my old Film P&S camera (Canon Prima AF-7) the only manual controls were to either stop the flash when auto wanted to use it or force the flash when auto didn't want to use it. Everything else was full automatic, focus & exposure. All you had to do is point (compose) and shot. And I took a lot of good shots with that P&S film camera some which I even have sold $300 large prints of.

Just like how DVD, Blue-Ray players, etc are way more complicated to use than old VCRs.

Technology is to supposed to make things simpler, but in a lot of cases, for example taking photos and watching a movie at home it's more complicated now-a-days.

Digital has not become more technical. What's happened is the same thing that's happened when anything becomes too democratized. There is always a push to start making it seem much more complicated than it is, so increasing numbers of people are turned off by it.

For example, web publishing and blogging is just as accessible to everyone today as they were 20 years ago. But then developers started rambling about W3C standards, cross-browser compatibility, etc. So people gave up this idea of web publishing and flocked to social media instead. Meanwhile, the ability to just sign up at a free blogging platform or a web host that makes it easy to create your own site never left. What changed was the perception, that unless you were a developer who knew every computer language inside and out and had read the W3C backwards and forwards, you couldn't build a website.

I went to art school to learn how to paint. I spent a year in a class getting bogged down in scientific theory about the physics of color and light. (For example, how objects don't contain any color but are really bouncing off specific wave lengths from the electromagnetic spectrum).

After getting fed up, I went to the library and picked up a few books on painting and the color wheel. And, well, whaddaya know? It all came down to learning the basic properties of color pigments (such as saturation, dullness, etc.) and how they could be mixed to match what I was seeing in front of me.

What I learned from this: when a person knows how to teach or illuminate others about something, he uses plain language. When he doesn't, he retreats behind jargon to talk over everyone's head, so that the issue isn't whether the person is being clear or not but whether everyone is just too stupid to understand what he's saying.

I think it's ok when someone wants to do something "as it comes"... as long as he doesn't do that for a living and/or it's nothing critical ("hey I'd like to try my hand at heart surgery today! wonder what this junk of flesh here does...").

Or, as long as he doesn't think he's a "master" when he can't even be bothered to understand the basics, and then proceeds to go all out on the internet rambling about what he thinks he knows on "focal length distortion", "how ISO affects exposure", even - *shudder* - "equivalence"...

FYI: Astronomical science CCD and CMOS use measures strongly linked to physics. There is no such thing as ISO.

CCD are characterized by: * spectral QE (science CCD are "mono")* read noise (in electrons)* dark current (e-/sec) at reference temperature and slope of e-/temp* pixel sizeThere are a few esoteric attributes (e.g. CIC) but the above are most significant. CCD gain is stated in e-/ADU (the linear inverse of video gain) but most CCD have fixed gain optimized for AD bit-depth (usually 16 bit) because CCD noise and such are invariant with gain.

CMOS are similarly characterized except:* gain affects read-noise (unlike CCD): lower gain has less noise but shallower depth. * CMOS has low-flux unstable correlated noise and many are Bayer only, so most CMOS are inappropriate for astro science though a few are acceptable (e.g. some ZWO).

But I don't see this approach being embraced by the photo crowd. ISO is more user friendly and I don't see a reasonable alternative.

@AstroStan"But I don't see this approach being embraced by the photo crowd. ISO is more user friendly and I don't see a reasonable alternative."So true. The highly tempting Gain and SNR are just as wrong.Maybe something real world like EQR (Exposure Quality Ratio, basically percentage of noise) or just N,I. (for Noise Index) ?I think it's with us until hardware swallows it up and makes it redundant; within two years, hopefully.

This article is complicated. Either I do not fully understand it or am not bothered to read and absorb all the details. All I know is that I up the ISO when I want smaller apertures, faster shutter speeds or the light is poor.

What ISO actually means now who cares as long as the required end results are still in sight?

I expose for the highlights on digital but the reason I can get satisfactory results is because my camera and its sensor have enough sensitivity and dynamic range.

From the 1950s aged nine, I was processing Pan F or Panatomic X in the Beutler compensating developer, or one of the similar Edwal's in my twelve years living in Toronto. They upped the ISO, tamed the contrast, gave a full range from highlights to shadows, beautiful smooth gradation and invisible grain.

You cannot do anything similar with digital. So, in some respects it is worse, in others far better. But It does not have that magic tonality of film you get with a Leica lens or another nearly as good.

What the author is trying to get at is open the aperture as wide as you can, but still holding your artistic intent. Also have the longest possible shutter speed that you can, without causing blur. Thus you will maximize the amount of light that hits the sensor, but make sute you haven't blown the high lights.Digital cameras have a base sensitivity. The ideal value. If your ISO is high and doesn't need to be for artistic intent with closed down aperture or fast shutter speed, than drop the IDO to maximize the light to yoir sensor.

That doesn’t seem to be what he’s really getting at with the article because those factors should and can be understood by anyone using a camera (ideally one should learn how to expose an image manually so that they truly understand aperture, ss, and film/sensor sensitivity).

It seems that Richard’s point is more that the digital cams we’re using aren’t even showing us what’s really being captured (in the Raw files) because all of the metering and feedback is reflecting what the JPEG output is going to be. And because of this it’s not easy to determine Proper exposure for Raws. Isn’t this part of what he’s getting at?

Or, underexpose to preserve more highlights if you have a modern sensor that sufficiently preserves shadow details. But in either case you have to make an educated guess about where (& how much of) your highlights are likely to clip.

What I'm trying to say is that the digital ISO standard isn't as directly analogous to the film standard as it appears. Furthermore it tells you nothing about what's going on at the Raw level. On top of this it has been broadened to the point of not telling you very much at all.

As sensors get better, the ability to use minimal amplification (or one of the two inherent gain modes) and then brighten later, plus the potential benefits of exposing to the right mean that the opacity brought to the process by this nominally familiar concept, risks holding us, our cameras and our photography back.

Personally, I think something clearer and more consistent (though ideally one that doesn't require much re-learning or changing of operation), would be good, along with at least the option of long-missing Raw-relevant exposure tools.

I too wish I have a RAW histogram in my camera (since a looong time). It should not be so difficult because there is not even a need to demosaic the bayer/xtrans grid.

That beeing said, most sensors are not completely invariant, meaning in my understanding that there is something beyond only brightening base ISO capture up to a mid-grey "correct" level. What I'd like to understand clearly is if there are cases where ETTR can be helpful beyond base ISO, if pushed ISO imply an amplification (even not necessarily in direct relationship with the ISO number).

BTW, I'd also like an ETTR shortcut button on my camera (with some kind of clipping tolerance setting). I use my exposure comp dial a lot but it is indeed very difficult with JPG histograms and warnings, plus a direct button would be so convenient.

On my D750 I use Neutral color setup which makes the JPEGs rendered with that setup but also the on camera histogram will show up with this file. NL (Neutral) is really very close to the RAW histogram.

I say, "Shoot JPEG and get the exposure right in the camera"! Just think of all the valuable time you can save by not having "a work flow" on the computer! You could actually be out shooting more photos instead! :-)

@bolt2014 it depends on when you have time.If you have time during the shooting, and are able to play with the various jpeg settings (highlight recovery, shadow correction, saturation, contrast sharpening etc. etc. etc.) on the spot, and are able to judge the result on the uncalibrated LCD of the camera, then by any means do it.

I personally am generally much more in a rush when taking pictures unfortunately, and have time when I get back home, where I can develop my RAWs on a profiled monitor, and spend as much time as I want on every single photo.

In the field, I only need to nail a good exposure by adjusting aperture and shutter speed, and select an appropriate ISO. I can concentrate on subject choice, composition and framing, I'm not locking down WB, and I don't even have to activate settings (like lens distortion correction) that slow down the camera.

@bolt2014 Agree. But my PC workflow starts with an auto-exposure adjustment, applied by default during import, which is not a PITA. On LCDs, I cannot nail exposure anyway, so at base ISO (most of my pictures), I ETTR to get as much useful information as I can in my RAW file, then I let the PC software auto adjust. Autotone is badly regarded but I think that it mainly comes from LR whose previous auto adjustments were very poor. It is better with the new algorithms and if you need a more flexible and quick approach, COP is your friend. For even more flexibility and fine tuning of auto exposure, Darktable is the best to my knowledge.

For the last two years or so I have been using FastRawViewer (FRV) which shows a histogram and extensive information from the RAW data, not the embedded JPEG. Using this, I have been amazed at how the dark art of shooting and using RAW has been turned into a more controlled exercise, rather than the alternative of haphazard guesswork.

Until a few weeks ago I used to spot meter on a mid-tone but now, on Iliah Borg's suggestion, I started to meter on the brightest part and up the EV adjustment by three stops. I did some tests and decided that +3 on my Nikon D610 would not result in burn out.

Typically, I am bracketing with three exposures so, with the EV +3 adjustment take two further exposures +4 and +5 (or, based on a typical mid-tone, more like 0, +1 and +2) to deal with those shadows when they are decidedly heavy.

The sensor in my camera generates little noise, so you can heavily up the gain in post-processing of under-exposed areas and get away with it. Secondly, you want shadows to look like shadows so, even after raising the threshold until there is some detail in them, even heavy under- exposure usually need not matter.

But still I am going to bracket quite often, just to play safe but not use the extra frames until I find that I really need them.

I am off on holiday from the UK in just over two weeks time, visiting, among other places, Zion National Park, Canyonlands and Arches where I expect the light to be brilliant and challenging, especially since I like to shoot towards the sun to get dramatic lighting.

But, as I just discovered, one frame will mostly be enough, given that I am metering on the highlights and setting the camera to +3 EV, maybe sometimes +4.

I was aware of the fires in CA but it had not occurred to me that I could be at risk where I am going. This summer has been unusually hot in many places around the world. In England, we have had temperatures well above normal and hardly any rain beyond a slight drip once or twice for five minutes since mid-June and are told it may continue for another three months. For me the only benefit is that I have acclimatised to US temperatures where I am going, well not quite but the humidity should be low which makes a huge difference.

I only just discovered that a good sensor can cope amazingly well, often in just one frame, but definitely with three.

Last night I rushed out of my front door to take some pictures into a very bright sky with some delightful clouds close to the direction of the setting sun. It was an ideal opportunity to test whether my recently adopted technique was precise enough not to blow out the highlights and also get enough detail in extremely heavy shadow and without suffering visible noise there too.

But, to my amazement, the exposure +4, based on a reading of the brightest parts, captured everything fine. The highlights were negligibly over-exposed in less than 0.44% of the pixels (as FRV shows) but because of so much very heavy shadow, over 50% was heavily under-exposed. Most of the image was hugely solid black until adjusted in software but when I did that I got a far better result from the one frame than using all three, even in such an extreme situation as this was.

Been also using fast raw viewer for a year, it's absolutely great. But we use it for events and weddings. As you said, after a short while you get to know which specific settings on your camera give you the best exposure.Plus we save so much time culling.

You absolutely don't need to be a great technician to take great photos. But if you're a good photographer, learning what's going on might help you improve the technical quality of the already great photos you take.

At which point, is it better to have a clear and consistent means of describing the camera's function or an opaque and inconsistent one?

It's more like you need to know how to hold a chisel and hammer if you want to get the best results. A camera is a tool, and you are an artist. You have to be one with your tool to do your best work. How can you do that if you don't know how it works inside and out?This "who cares how it works, as long as it does" attitude is actually a rather bad trend in our society, but that's a different story.

Right, we're not getting to the level of quantum mechanics here ;) But ISO is a fundamental thing to know about the operation of a digital camera. Even with computers, when I was learning how to do CGI, I still had to learn about such things as defragmenting my drive frequently to make things run smoother, batching processing tasks, running scripts etc. Do you need to know all that to do good work? No, but it makes you better and more efficient at what you do.

In reply to Jeff Greenberg, I would say much the same as Richard Butler, leaving out the three words below I have put in between [ and ]:

"You absolutely don't need to be a great technician to take great photos. But if you're a good photographer, learning what's going on might help you improve the [technical] quality of the [already great] photos you take.

At which point, is it better to have a clear and consistent means of describing the camera's function or an opaque and inconsistent one?"...

Except that, instead of his last paragraph, I would say

"If your interest is only casual spend a smaller sum on a more modest camera, one still of good quality, and why bother with DP Review? If you spend a lot on your equipment, either you are wasting money or not actually interested in using your equipment remotely close to its potential".

I guess for clipping the highlights, either in an EVF or backscreen you could have the clipped highlights flash as a warning? And the exposure compensation can be used to preserve more of the clipped highlights?

I guess I don't really know what the ISO amplification does. I'd have to read up more on that.

For histograms . . . if based off of RAW, I guess you could use that to help you manually set exposure to do ETTR.

And for tone mapping . . . if shooting RAW, it only saves your preference? But this can be overridden either in-camera or in Lightroom for each individual image?

I have had a lot to say, so think I will have to quieten down after this.

I do very much like all of what lélé says. My ideal camera would have all this this incorporated...

except that it would display the RAW histogram before exposure on the LCD but definitely not in an EVF.

It would be a DSLR and a button would allow the histogram to be seen in the viewfinder, with a menu setting to choose the overlay with a choice of the percentage opacity of the display on top of the viewfinder image or even 100% to momentarily entirely replace it.

One of the things I'm beginning to realize as I get older is that there is a generation of people who don't understand the concept of technological parity. Their logic is that if the mechanics between two different types of technologies are different, then the concepts and functionality between them are different, even though they are conceptually and functionally the exact same thing.

For example, a word processor is a completely different technology from a typewriter and the mechanics behind it are different. When you type a document out, it appears as one interrupted page. But when you print out multiple pages from that document, the separate pages aren't "metaphors" for how typewriters could only allow you to type one page at a time. It's the ability to produce pages using mechanics and technology completely different from when you had to manually type them out page by page.

PT. 2. The same fallacy is at hand with this whole digital vs analog ISO nonsense. The mechanics and technology behind how each works are completely different, but the concept and the functionality are exactly the same. To call digital ISO a metaphor is absurd. It's not understanding that digital is using different methods to create ISO in digital and is the exact equivalent of what it was in film.

That's an interesting perspective. I'd like to add a few things to consider, though:

1) They aren't quite parallels: ISO in film was designed to help you get a printable negative, ISO in digital essentially jumps straight to the print makes a lot of assumptions about the steps in between. This is unhelpful for anyone shooting Raw, since they're not necessarily going to that same destination.

2) ISO in film worried about exposure and developing, which limited the number of assumptions. ISO in digital combines exposure, hardware amplification and tone curve. This adds an extra variable and hides how much of each is at play.

3) ISO and its associated metering, helped you deliver a known end-point. Post 2006, the REI variant of the ISO standard effectively lets the manufacturer decide what 'correct' looks like. It's not something that can be tested or measured.

@tmp, I'm not ignoring any truth; you just don't understand why ISO varies from camera to camera.

The reason why ISO varies has to do with the fact that cameras don't come equipped with the same size and type of sensor (CCD vs CMOS), as well as different ratios in terms of sensor size vs megapixel count.

It's why you might start seeing heavy noise above 400 ISO in a tiny pocket camera that has a tiny sensor and 20MP count but don't start seeing any noise above 800 ISO in a prosumer camera with a large sensor and smaller MP count.

The reason why goes back to my early analogy about word processors and typewriters. All I'm hearing from you is this: "You don't understand the concept of pages, because the way you made pages in a typewriter is completely different from how you make them in Microsoft Word; therefore, you have to readjust your thinking about what a page is in order to produce one properly."

Another reason why I don't understand what you're saying is that I made the transition from film over 10 years ago (see my profile). Much better photographers than I could ever be made the switch for far longer. Combined, everyone who's made the switch to digital in all this time have produced billions of photographs without struggling to properly expose photographs within this "wrong" way of thinking about ISO.

But somehow, it's not you who's got the concept of ISO wrong; it's everyone else? Including Pulitzer Prize-winning photographers?

Thank you for very much for responding. But there is a problem. Again, you keep making the argument that because the technology is different between analog and digital ISO (and the intent behind them), the *concept* people have of ISO in the digital age is wrong.

If you want to argue that people have to have a better understanding of how ISO works in digital because it works differently than it did in analog, that is something I wholeheartedly agree with. For example, creating a playlist on your mp3 player is completely different from creating one on a jukebox. Because of this, you have to understand how the technology differs between the jukebox and an mp3 player so you can finally make one on your player successfully.

In other words, you can't go, "Since this mp4 player has a playlist function, it works like a jukebox." No. It's not coin-operated, and it uses digital rather than vinyl. It's meant to be listened to privately as opposed to publicly.

So, yes, since an mp3 playlist works differently from a jukebox, it's important to make the distinction between the two.

Yet when all is said and done, the concept of the playlist remains the same in the mp3 player as it did in the jukebox because that is what an mp3 playlist is supposed to be, the digital equivalent of a jukebox. Not a metaphor. The digital equivalent.

A person can be said to misunderstand how the playlist works in an mp3 player as opposed to a jukebox, but they can't be said to misunderstand what a playlist is, what its function is or what it means conceptually.

That's exactly his point though. They are not serving the same function. The function of ISO in film was to increase sensitivity. In digital it can increase sensitivity (amplification) OR simply make the existing image brighter (tone mapping) OR both! Saying that the end result is a brighter image in both film ISO and digital ISO is not at all useful in this case. It's like comparing a CRT to an LCD and saying that because both are screens, understanding the underlying technology and its limitations is not important because in the end both just produce an image.

"Make everything as simple as possible, but not simpler." Albert Einstein Technological parity only exists where it does. Don't become so married to the elegance of a statement, that you ignore what doesn't fit.

ISO applies to camera jpeg, not raw. An example: many cameras have a dynamic range/highlight preserving setting. The camera will shoot, for argument’s sake, as if the ISO were manually set to, say, 100, but underexpose and digitally bring up the shadows and mid tones for the JPEG. Because the camera JPEG is lightened this way, the camera will label the EXIF as, say, ISO 320. However, the RAW, as can be seen when you view it in a RAW editor, is darker, and is the same RAW that you would get from setting the camera to shoot at ISO 100 (in this example) and simply underexposing.

Turning up the ISO and getting more noise from the camera's gain stages is like turning up your stereo and getting more hiss from the audio gain stages. Not hum from the power supply or external inductive pickup.

Please, if you're going to fling comparative metaphors around, make sure you have some idea what you're talking about first.

Also, certainly you can get more noise when there are amplifier stages that generate noise, and gain is applied to their output. Any remarks to the contrary are outright wrong.

"getting more noise from the camera's gain stages is like turning up your stereo and getting more hiss from the audio gain stages. Not hum from the power supply or external inductive pickup." - that's if the additional amount of noise is significant compared to the noise from other components, and not negligible. Do you have numbers to support the "likeness"?

fyngyrz - You're quite right: I took a commonly-used laymen's description of the problem without checking what the correct terminology should be. I've re-phrased that section accordingly.

The underlying point remains: most people have heard more noise if they turn up their amplifier and assume that the same thing is happening with ISO. It isn't. As Iliah says, most of the noise is present in the signal before it's amplified: it's not coming from the amplification process itself.

These days, a well designed amplifier has an SNR of 80dB or more. You won't hear hiss from the amp. The hiss you hear is very similar to what you see in a high ISO photo - shot noise, examined closely enough to be perceptible (whether audibly or visually).

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Latest buying guides

If you want a compact camera that produces great quality photos without the hassle of changing lenses, there are plenty of choices available for every budget. Read on to find out which portable enthusiast compacts are our favorites.

Whether you're hitting the beach in the Northern Hemisphere or the ski slopes in the Southern, a rugged compact camera makes a great companion. In this buying guide we've taken a look at nine current models and chosen our favorites.

What's the best camera for under $500? These entry level cameras should be easy to use, offer good image quality and easily connect with a smartphone for sharing. In this buying guide we've rounded up all the current interchangeable lens cameras costing less than $500 and recommended the best.

If you're looking for a high-quality camera, you don't need to spend a ton of cash, nor do you need to buy the latest and greatest new product on the market. In our latest buying guide we've selected some cameras that while they're a bit older, still offer a lot of bang for the buck.

Whether you're new to the Micro Four Thirds system or a seasoned veteran, there are plenty of lenses available for you. We've used pretty much all of them, and in this guide we're giving your our recommendations for the best MFT lenses for various situations.

Blackmagic has announced an update to Blackmagic RAW that adds support, via plugins, to Adobe Premiere Pro and Avid Media Composer. Blackmagic also announced a pair of Video Assist 12G monitor-recorders with brighter HDR displays, USB-C recording and more.

Sony has announced the impending arrival of its next-generation video camera system, the FX9. The full-frame E-mount system is set to be released later this year with a 16-35mm E-mount lens to follow in spring 2020.

The Canon G5 X Mark II earns a Silver Award with its very good image quality, flexibility and the overall engaging experience of using the camera. However, if you need the very best in autofocus and video, other options may suit you better. Find out all the details in our full G5 X II review.

The Fujifilm X-A7 is the newest addition to the company's X-series lineup. Despite its relatively low price of $700 (with lens), Fujifilm didn't skimp on features. Click through to find out what you need to know about the X-A7.

The entry-level Fujifilm X-A7 improves upon many of its predecessor's weak points, including a zippier processor, an upgraded user experience and 4K/30p video capture. It goes on sale October 24th for $700 with a 15-45mm F3.5-5.6 kit lens.

Robert Frank's unconventional approach to photography and filmmaking defied generational constraints and inspired some of the most influential artists of the 20th century. He passed away today at age 94.

All three devices offer a standard 12MP camera plus, for the first time on an iPhone, an ultra-wide 13mm camera module. The 11 Pro and 11 Pro Max also retain the telephoto camera of previous generations.

Phase One's new XT camera system incorporates the company's IQ4 series of digital backs with up to 151MP of resolution and marries them to a line of Rodenstock lenses using the new XT camera body. The result is an impressively small package for one of the largest image sensors currently on the market - take a closer look here.

Phase One has announced its new XT camera system, which includes an IQ4 digital back, body (made up of a shutter release button and two dials) and a trio of Rodenstock lenses. The company is marketing the XT as a 'travel-friendly' product for landscape photographers.